1. Field of the Invention
This invention relates generally to improvements in tourniquet pressure monitors and, more particularly, but not by way of limitation, to a tourniquet pressure monitor having means to provide an alarm when the tourniquet pressure falls below or rises above predetermined minimum and maximum pressure levels, respectively, and a visually perceivable indication of the total time during which the tourniquet has been pressurized.
2. Description of the Prior Art
The use of the tourniquet to facilitate extremity surgery with a bloodless field has been common practice for years. Although the Esmarch bandage represented a significant improvement over the original screw-compression tourniquet devised by Petit in 1718, it was virtually impossible to control the degree of pressure exerted by the Esmarch bandage. This limitation when coupled with the destructive shearing force resulting from the rotational application of such a bandage, makes even the improved form of the Esmarch bandage devised by Von Langenbeck a truly dangerous means of obtaining a bloodless field for surgery in an extremity.
Following the introduction of the pneumatic tourniquet by Harvey Cushing, it was still common to have severe complications such as nerve palsy result from tourniquet use. Several studies have been published showing this damage to be a result of a localized block to conduction in the area where the tourniquet has been applied, with normal conduction occuring both proximally and distally in both sensory and motor fibers, thus establishing that the damage is a result of local compression of the nerve rather than ischemia. As a result of the determination that such damage is frequently the result of excessive pressure in the tourniquet system due to a faulty gage, it has been recommended that the pneumatic tourniquet gage be calibrated each day. Unfortunately, such daily calibration is often unperformed due to the heavy work load imposed upon operating room personnel.
In addition to the necessity of keeping the tourniquet pressure below a maximum pressure level, it is also important to prevent the tourniquet pressure from dropping to a level between systolic pressure and venous pressure thereby causing congestion which may be more harmful to the tissues distally then ischemia. Although the anesthetist is traditionally tasked with monitoring the tourniquet pressure, it is to be recognized that this function frequently suffers in view of the anesthetist's primary duty of administering the anesthetic.
In addition to nerve palsy, prolonged use of the pneumatic tourniquet may result in damage due to excessive ischemia time. Although it is generally agreed that ischemia time should be limited to two hours, times up to four hours have been reported without clinical evidence of permanent damage. In any event, the surgeon is responsible for deciding the maximum ischemia time at the beginning of each use of the tourniquet. However, the responsibility for monitoring ischemia time is usually delegated to one of the other operating room personnel, and has frequently been inadequately or inaccurately performed.